Lactic acid bacteria (LAB) have been consumed safely by humans in various fermented food and dairy products. Many of these LAB hold a “Generally Recognized as Safe” (GRAS) status and can be consumed at levels approaching 1 trillion cells per gram of food, without adverse effects. Selected members of the LAB are acid tolerant, but bile sensitive, and do not survive passage through the gastrointestinal tract. Thus, bile exposure of selected LAB can result in disruption of cellular integrity, permeabilization, and release of intracellular proteins. Such microbes can be orally delivered through the stomach to the small intestine for targeted delivery of biotherapeutic peptides upon permeabilization of the microbe by bile. In addition, the microbe dies upon bile permeabilization and would, therefore, remain contained within the GI tract following oral delivery.
Streptococcus thermophilus, is a gram-positive lactic acid bacterium of the viridans group. St. thermophilus is commonly found in fermented milk products including yogurt, fermented milk, and cheese. Commercial dairy products comprising St. thermophilus can be used as a treatment for antibiotic-associated diarrhea (Hickson, 2007, 335(7610):80).
Clostridium difficile (C. difficile) is the most common cause of nosocomial bacterial diarrhea and accounts for 10-20% of the cases of antibiotic-associated diarrhea. C. difficile infection can result in asymptomatic carriage, mild diarrhea, or fulminant pseudomembranous colitis. This anaerobic bacterium causes intestinal damage primarily through the actions of two large exotoxins, toxin A and toxin B. Purified toxin A (TxA) causes intestinal secretion, destruction of the intestinal epithelium and hemorrhagic colitis when introduced in vivo to the intestinal lumen. The mechanism of TxA-induced enteritis involves toxin binding to enterocyte receptors, leading to activation of sensory and enteric nerves that results in enhanced intestinal secretion and motility, degranulation of mast cells, and infiltration of the mucosa by neutrophils. In addition to its proinflammatory and prosecretory activities, TxA induces apoptosis and nonapoptotic cell death, which could contribute to intestinal mucosal disruption. Specifically, TxA has been shown to affect important aspects of the intestinal mucosal repair process such as epithelial cell migration, apoptosis, and the development of transepithelial resistance (Brito et al. (2005) Dig Dis and Sci 50(7): 1271-1278).
Glutamine (Gln) is the primary fuel for both enterocyte and the colonocyte and is necessary for the maintenance of intestinal structure in both normal and stressed states (Cario et al., Eur J Clin Invest. 2000 May 30(5):419429). Studies have shown glutamine supplementation to prevent villous atrophy, and bacterial translocation, conditions associated with standard parenteral nutrition (Van Der Hulst et al., Lancet 1993 341:1363). Glutamine plays a pivotal role in several metabolic pathways. Its importance in tissue culture has long been recognized, and it is a key nitrogen donor for the biosynthesis of nucleotides, amino sugars, and amino acids in mammalian cells. It is anticipated that the availability of glutamine will be especially important during persistent diarrhea and malnutrition, when the mucosal barrier function is often disrupted. Animal studies have shown that glutamine-enriched nutrition can attenuate bacterial translocation, improve nutritional status, decrease intestinal injury and result in improved survival in a lethal model of methotrexate-induced enterocolitis.
Alanyl-glutamine (Ala-Gin) is a stable glutamine derivative that has been shown to be much more stable in acidic water solutions (such as they would be expected to face in a patient's stomach or intestine) and to drive salt and water absorption comparable to, if not better, than glucose (see U.S. Pat. No. 5,561,111, the disclosure of which is expressly incorporated herein). Stable glutamine derivatives are useful not only in malnourished children with diarrhea, but also in patients kept too long on parenteral (IV) fluids or tube feedings or in those with damaged intestinal mucosa from infection or chemotherapy.